Causes of the Russian heat wave and Pakistani floods

The Great Russian Heat Wave of 2010 is one of the most intense, widespread, and long-lasting heat waves in world history. Only the European heat wave of 2003, which killed 35,000 - 50,000 people, and the incredible North American heat wave of July 1936, which set all-time extreme highest temperature records in fifteen U.S. states, can compare. All of these heat waves were caused by a highly unusual kink in the jet stream that remained locked in place for over a month. The jet stream is an upper-level river of air, between the altitudes of about 30,000 - 40,000 feet (10,000 - 12,000 meters). In July over Europe and Asia, the jet stream has two branches: a strong southern "subtropical" jet that blows across southern Europe, and a weaker "polar" jet that blows across northern Europe. The polar jet stream carries along the extratropical cyclones (lows) that bring the mid-latitudes most of their precipitation. The polar jet stream also acts as the boundary between cold, Arctic air, and warm tropical air. If the polar jet stream shifts to the north of its usual location, areas just to its south will be much hotter and drier than normal. In July 2010, a remarkably strong polar jet stream developed over northern Europe. This jet curved far to the north of Moscow, then plunged southwards towards Pakistan. This allowed hot air to surge northwards over most of European Russia, and prevented rain-bearing low pressure systems from traveling over the region. These rain-bearing low pressure systems passed far to the north of European Russia, then dove unusually far to the south, into northern Pakistan. The heavy rains from these lows combined with Pakistan's usual summer monsoon rains to trigger Pakistan's most devastating floods in history.

Figure 1. Winds of the jet stream at an altitude of 300 millibars (roughly 30,000 feet high). Left: Average July winds from the period 1968 - 1996 show that a two-branch jet stream typically occurs over Europe and Asia--a northern "polar" jet stream, and a more southerly "subtropical" jet stream. Right: the jet stream pattern in July 2010 was highly unusual, with a very strong polar jet looping far to the north of Russia, then diving southwards towards Pakistan. Image credit: NOAA/ESRL.

What caused this unusual jet stream pattern?The unusual jet stream pattern that led to the 2010 Russian heat wave and Pakistani floods began during the last week of June, and remained locked in place all of July and for the first half of August. Long-lived "blocking" episodes like this are usually caused by unusual sea surface temperature patterns, according to recent research done using climate models. For example, Feudale and Shukla (2010) found that during the summer of 2003, exceptionally high sea surface temperatures of 4°C (7°F) above average over the Mediterranean Sea, combined with unusually warm SSTs in the northern portion of the North Atlantic Ocean near the Arctic, combined to shift the jet stream to the north over Western Europe and create the heat wave of 2003. I expect that the current SST pattern over the ocean regions surrounding Europe played a key role in shifting the jet stream to create the heat wave of 2010. Note that the SST anomaly pattern is quite different this year compared to 2003, which may be why this year's heat wave hit Eastern Europe, and the 2003 heat wave hit Western Europe. Human-caused climate change also may have played a role; using climate models, Stott et al. (2004) found it very likely (>90% chance) that human-caused climate change has at least doubled the risk of severe heat waves like the great 2003 European heat wave.

Figure 2. A comparison of the departure of sea surface temperature (SST) from average just prior the the start of the great European heat waves of 2003 and 2010. Temperatures in the Mediterranean Sea were up to 4°C above average in 2003, which has been implicated as a major cause of the Western European heat wave of 2003. Image credit: NOAA/NESDIS.

The World Meteorological Organization (WMO) has posted an analysis of the recent extreme weather events, concluding, "the sequence of current events matches IPCC projections of more frequent and more intense extreme weather events due to global warming."

Moscow sees real relief from the Great Russian Heat Wave of 2010For the first time in more than a month, temperatures at Moscow's Domodedovo airport failed to exceed 30°C (86°F) today. Clouds and thunderstorms blew into the city this morning, keeping the high temperature down to just 29°C (84°F). This breaks a string of 35 straight days when the temperature reached 30°C. At Moscow's official observing site, the Moscow Observatory, this string was 30 days. Moscow's average high temperature for August 13 is 20°C (68°F), so today's temperatures were still well above normal. However, today's cool-down marks the beginning of the end for Russia's great heat wave. The latest forecast for Moscow calls for high temperatures below 30°C for the coming week, and Moscow may not exceed that threshold for the remainder of summer. Long range forecasts from the ECMWF and GFS models continue to suggest that a series of troughs of low pressure will attack the ridge of high pressure anchored over Russia, bringing cooler temperatures just 5°C (8°F) above average to Russia late next week. By ten days from now, the ECMWF model shows a strong trough of low pressure over Moscow, and a end to the Great Russian Heat Wave of 2010. Moscow still has to concern itself with smoke from the wildfires burning southeast of the city; winds are expected to shift early next week and bring the smoke towards the city again. However, the cooler weather should aid fire-fighting efforts, so the smoke problems should not be as bad as last week's nightmare.

Figure 2. Image from NASA's Aqua satellite of smoke from wildfires burning to the southeast of Moscow yesterday, August 12, 2010. Northerly winds were keeping the smoke from blowing over the city. Image credit: NASA.

The tropics are quietThe remnants of Tropical Depression Five continue to bring heavy rain to portions of Southeast Louisiana today. Up to five inches of rain has fallen in regions near New Orleans. The GFS model predicts that the remains of TD 5 could move off the coast of Mississippi by the middle of next week and regenerate, but none of the other models is making this forecast. Both the GFS and ECMWF models are predicting that a tropical storm will develop off the coast of Africa by next Friday, August 20.

Donations urgently needed in PakistanThe devastation wrought by the worst flooding in Pakistan's history requires a huge response by the international community. Wunderblogger Dr. Ricky Rood, author of our Climate Change Blog, has a friend working in Pakistan who underscored the desperate situation there:

This is the worst natural disaster in the history of Pakistan in terms of number of people and area affected. Although not as many people have been killed as in the 2005 earthquake, we have already nearly 900,000 displaced persons thus far just in Khyber Pakhtunkhwa. Crops are destroyed; shops, hotels, and other business have simply been swept away in Swat, which had just this year been cleared of Taliban and was on the way to recovery; and districts closer to Peshawar and parts of Peshawar district are still, or perhaps again after yesterday/today, under water. After the immediate emergency response, it will be years of rebuilding to replace what has been lost and to start to develop again. I know you have the power to control the weather, so if you cold give us a week or two without more rain at least we could keep the helicopters flying and give people a chance to go to their homes, recover what might still be there, set up tents if we can get enough to them, and start to clean up."

She gave the following recommendations for charities that do work in the flood-ravaged zone, and are effective at getting aid to those who need it the most:

anyhow looking at the satellite over the gulf and bahamas, it really doesn't look like august to me.. with cold fronts dropping into the mid atlantic, and extreeme shear running things across that area..

Anyway, Kori, the EURO has been hinting at positive NAO on the 00z run and strongly negative on the 12z run. Not really sure which one to believe at this point.

I've been meaning to check its NAO forecast. I have the website, but I keep forgetting. I'll start doing that routinely now.

But in light of what you said, it only further confirms my earlier assessment of the situation: the synoptic scale steering pattern is highly uncertain at this juncture. The models cannot decide if there will be more 500 mb troughing or ridging.

Quoting xcool:BACK TO OUR DEVELOPING SFC LOW...ALL FORECAST MODEL TAKE THE LOWCENTER BACK OVER THE GULF AND HAVE IT TAKING ON TROPICALCHARACTERISTICS AS IT BECOMES WARM CORE. THIS IS THE REASON MOSTCONTINUE TO DEEPEN THE FEATURE AS IT MOVES WEST IN A VERY FAVORABLEUPPER LEVEL ENVIRONMENT. IF THE SYSTEM DOES DEVELOP AS A TROPICALENTITY...THEN THERE WILL BE SOME IMPACTS TO THE CWA.ADDITIONALLY...UNTIL IT DEVELOPS...FORECAST MODELS WILL CONTINUE TOHAVE TROUBLE WITH TIMING AND ANY CONSISTENT TRACK. ATLEAST THERE ISA STRONG CONSENSUS AMONG THE MODELS AND WE HAVE A GOOD HANDLE ONTHE GENERAL EVOLUTION OF THE FEATURE BETWEEN TUE-WED. MOST OF THEIMPACTS FOR OUR AREA WOULD BE FROM HEAVY RAINFALL IF PERSISTENTBANDS CAN DEVELOP AND TRAIN. ALSO...IF IT CAN DEEPEN ENOUGH...THENTHE LOW LEVEL SHEAR WILL INCREASE TO A POINT THAT CAN SUPPORTROTATING UPDRAFTS. THIS SEEMS POSSIBLE ON WED AT THIS TIME.

Quoting xcool:BACK TO OUR DEVELOPING SFC LOW...ALL FORECAST MODEL TAKE THE LOWCENTER BACK OVER THE GULF AND HAVE IT TAKING ON TROPICALCHARACTERISTICS AS IT BECOMES WARM CORE. THIS IS THE REASON MOSTCONTINUE TO DEEPEN THE FEATURE AS IT MOVES WEST IN A VERY FAVORABLEUPPER LEVEL ENVIRONMENT. IF THE SYSTEM DOES DEVELOP AS A TROPICALENTITY...THEN THERE WILL BE SOME IMPACTS TO THE CWA.ADDITIONALLY...UNTIL IT DEVELOPS...FORECAST MODELS WILL CONTINUE TOHAVE TROUBLE WITH TIMING AND ANY CONSISTENT TRACK. ATLEAST THERE ISA STRONG CONSENSUS AMONG THE MODELS AND WE HAVE A GOOD HANDLE ONTHE GENERAL EVOLUTION OF THE FEATURE BETWEEN TUE-WED. MOST OF THEIMPACTS FOR OUR AREA WOULD BE FROM HEAVY RAINFALL IF PERSISTENTBANDS CAN DEVELOP AND TRAIN. ALSO...IF IT CAN DEEPEN ENOUGH...THENTHE LOW LEVEL SHEAR WILL INCREASE TO A POINT THAT CAN SUPPORTROTATING UPDRAFTS. THIS SEEMS POSSIBLE ON WED AT THIS TIME.

BACK TO OUR DEVELOPING SFC LOW...ALL FORECAST MODEL TAKE THE LOWCENTER BACK OVER THE GULF AND HAVE IT TAKING ON TROPICALCHARACTERISTICS AS IT BECOMES WARM CORE. THIS IS THE REASON MOSTCONTINUE TO DEEPEN THE FEATURE AS IT MOVES WEST IN A VERY FAVORABLEUPPER LEVEL ENVIRONMENT. IF THE SYSTEM DOES DEVELOP AS A TROPICALENTITY...THEN THERE WILL BE SOME IMPACTS TO THE CWA.ADDITIONALLY...UNTIL IT DEVELOPS...FORECAST MODELS WILL CONTINUE TOHAVE TROUBLE WITH TIMING AND ANY CONSISTENT TRACK. ATLEAST THERE ISA STRONG CONSENSUS AMONG THE MODELS AND WE HAVE A GOOD HANDLE ONTHE GENERAL EVOLUTION OF THE FEATURE BETWEEN TUE-WED. MOST OF THEIMPACTS FOR OUR AREA WOULD BE FROM HEAVY RAINFALL IF PERSISTENTBANDS CAN DEVELOP AND TRAIN. ALSO...IF IT CAN DEEPEN ENOUGH...THENTHE LOW LEVEL SHEAR WILL INCREASE TO A POINT THAT CAN SUPPORTROTATING UPDRAFTS. THIS SEEMS POSSIBLE ON WED AT THIS TIME.

The GFS had it hitting Florida at 6z, though. Remember that. Then at 12z it had it recurving. It's not surprising to see the ECMWF flipflopping as well. It only proves how uncertain the long-range synoptic scale steering pattern is. Like I said, both the two scenarios are equally plausible right now, until the picture becomes clearer.